Urinary Obstruction in Cats

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  • What is a urinary obstruction?

    Medically known as ischuria, a urinary obstruction (UO or FUO) is a medical emergency requiring immediate treatment. It occurs when the flow of urine is blocked anywhere along the urinary tract.

    Causes of urinary obstructions in cats

    Struvite crystals in a cat urine sample

    53% of obstructions are idiopathic (no known cause), fewer cases are caused by uroliths or urethral plugs which contain mucus, protein, cellular debris, sloughed off epithelial cells and crystals (commonly struvite) in the core.

    • Urinary crystals: Crystals form when the urine is too alkaline or acidic and is medically termed crystalluria. The most common crystals to occur in cats are struvite which develops in alkaline urine or calcium oxalate which tend to form when the urine is too acidic.
    • Uroliths (stones): Rock like stones in the bladder develops when crystals grow in size and combine with organic material in the bladder to form a stone.
    • Inflammation (urethritis): Inflammation can occur due to crystals, urinary tract infection, trauma, prostate infection or cancer.
    • Scar tissue: Scar tissue develops due to a previous blockage in the urinary tract which causes a thickening and narrowing of the urethra.
    • Tumours: Benign or cancerous tumours of the bladder neck or urethra can cause it to narrow.
    • Blood clots:  These can form in the bladder and cause a blockage as they travel down the urethra which can be related to trauma. I recently read an article about a cat who was found hunched in somebody’s garden. He was taken to a veterinarian who diagnosed a urinary blockage. A catheter was inserted and bloody urine was drained from the bladder along with blood clots. It was later discovered the cat also had a broken pelvis, the trauma had caused blood clots to develop in the bladder.

    cat bladder and kidneys

    Males are at increased risk due to their longer urethra (the tube which drains urine from the bladder through and out of the penis) which narrows inside the penis. However, blockages can develop in females too.

    Left untreated, an obstruction can lead to a ruptured bladder and/or a uremic crisis as the kidneys are no longer functioning as they should, toxic levels of nitrogenous waste products (uremia) and potassium (hyperkalemia) build up in the blood and metabolic acidosis develops. It can take as little as 24 hours for this to occur.

    A distended bladder can also cause the bladder to lose its tone (bladder atony), resulting in urinary incontinence, which may be permanent. Urinary obstruction can occur in cats of all ages, although it is more common in adult male cats.

    What causes crystal and stone formation?

    We know that 53% of blockages are idiopathic, the most common known causes are uroliths and urethral plugs. There are several likely causes of their formation.

    • Diet – This has long been suspected due to the popularity of dry foods over the past 20 years. These diets often change the pH of your cat’s urine, making a more favourable environment for urinary crystals to develop. Dry food only contains a small amount of water compared to a wet diet (raw or canned) which is approximately 70% water. Many cats don’t make up for this imbalance by drinking more, so a cat on dry food will often have very concentrated urine due to inadequate intake. Supersaturated urine is more likely to result in the formation of urinary crystals.
    • Stress – There are two possible reasons why stress can lead to a blockage. Some stressful situations are the result of inter-cat aggression, which can spill over to litter tray usage. The stressed cat may delay going to the toilet for several reasons, leading to his urine becoming more concentrated which provides the ideal medium for crystal formation. Chronic stress can also trigger bladder inflammation which can produce large amounts of inflammation and debris.
    • Portosystemic shunt is a congenital disorder in which blood shunts around the liver instead of through as the liver is responsible for the detoxification of blood, toxins, including ammonia, build-up, which can lead to the formation of ammonium biurate crystals in the urine


    Initially, there may be an incomplete blockage which means your cat can urinate but with difficulty and often with associated pain. Outdoor cats typically present in an advanced state because it is harder for the owner to monitor urine output and may miss early symptoms.

    Early warning signs:

    The plug will continue to collect debris until it completely blocks the urethra. Once a complete blockage has occurred, the cat is in danger unless quickly unblocked.

    Complete blockage:

    A completely blocked cat is in a great deal of pain and discomfort. You may be able to feel the distended bladder towards the rear unless it has ruptured. This is a medical emergency, and veterinary attention is vital to unblock your cat.

    • Inability to urinate (many pet owners confuse this with constipation)
    • Sand like material at the tip of the penis
    • Frequent trips to the litter tray
    • Crying when trying to go to the toilet
    • Abdominal pain
    • Abdominal swelling
    • Hiding
    • Hunched over appearance
    • Lethargy
    • Pain and/or aggression when touched
    • Loss of appetite

    Additional symptoms may occur as the kidneys fail and toxins and potassium build up in the blood. These may include vomiting, loss of appetite, weakness, dehydration, lethargy, abnormal heart rhythm, drunken gait, neurological disturbances, bradycardia (slow heartbeat) and ultimately collapse. Anchor


    Your veterinarian should be able to make a tentative diagnosis based on presenting symptoms. He will perform a complete physical examination, at which time he will be able to feel a firm, full bladder, there will also be abdominal pain or discomfort.

    Diagnostic workup:

    • Blood profiles to check blood potassium, creatinine and nitrogen levels and assess the kidneys for damage, look for signs of infection or systemic disease.
    • Urinalysis to look for infection and crystals in the urine and determine what type they are.
    • X-ray or ultrasound to evaluate for stones, congenital abnormalities, and tumours.
    • ECG (electrocardiogram) to monitor heart rhythm.


    Anchor There are several steps involved in unblocking the cat.

    1. Stabilise the cat (treat electrolyte imbalances)
    2. Unobstruct the cat (cystocentesis or catheter)
    3. Supportive care such as pain medication and fluid therapy as well as regular ECG to monitor the heart

    Emergency treatment:

    • Lower potassium levels: The first priority is to correct electrolyte derangements. Treating hyperkalemia with calcium gluconate which antagonises the effect of hyperkalemia on the heart. Insulin/dextrose can help to shift potassium into the cells and sodium bicarbonate raises blood pH which also drives potassium into the cells.
    • Catheterisation: To allow the bladder to void urine, the catheter be in place for several days afterwards. Heavy sedation is necessary to catheterise the cat, which involves the insertion of a thin tube into the penis and up to the bladder. A sterile solution is flushed through the tube to push the obstruction back into the bladder, where it will dissolve or be surgically removed.

    Medical management:

    Once the obstruction has been removed, the kidneys can resume their job of urine production, removing toxins from the bloodstream. In the days after, urine production is increased (post-obstructive diuresis) as the kidneys cleanse the blood. Intravenous fluids will be continued to prevent dehydration and electrolyte derangements such as hypokalemia (low blood potassium) due to increased urine output.

    • During this time, the catheter will remain in place, and the veterinarian will monitor urine output.
    • Painkillers to relieve discomfort.
    • Antispasmodic medications such as Prazosin to relax the urethra.
    • Antibiotics, if indicated.

    Addressing the underlying cause will be necessary to prevent future occurrences. Increase water consumption to dilute the urine and feed a canned or raw diet as this contains a higher amount of water than dry food.

    • Dissolving crystals: If your cat has urinary crystals, your veterinarian can prescribe a prescription diet such as Hills c/d or s/d to dissolve them and maintain urine pH.
    •  Cystomy: Surgical removal of the stones that are too large to be dissolved or flushed out. This procedure involves opening the bladder to remove the stones under a general anesthetic.

    Once the stones have been removed, they will be sent off to determine the type, and culture will be performed to determine what (if any) bacteria are also present so the most suitable antibiotic can be prescribed.

    • Perineal urethrostomy: Surgery to remove the penis and create a new opening in the wider portion of the urethra, subcutaneous tissue and skin in the perianal region (between the perennial and anus). This wider opening allows plug like substances to pass out of the body, avoiding a blockage.


    Follow instructions and administer medication as prescribed. Keep a close eye on the cat’s litter tray usage and take him straight to the veterinarian if he shows signs of blockage.

    Increasing water consumption is important to keep the urine as dilute as possible, which decreases the chances of crystal formation.

    Switch to a wet diet and encourage your cat to drink by adding more water bowls or introducing a water fountain bowl, which many cats love.

    Keep the cat as stress-free as possible to reduce the chances of a recurrence.

    Keep litter trays scrupulously clean, remove solids twice a day and empty once a week. Provide several trays for multi-cat households. The general rule of thumb is one tray per cat, plus one extra.


    • Julia Wilson, 'Cat World' Founder

      Julia Wilson is the founder of Cat-World, and has researched and written over 1,000 articles about cats. She is a cat expert with over 20 years of experience writing about a wide range of cat topics, with a special interest in cat health, welfare and preventative care. Julia lives in Sydney with her family, four cats and two dogs. Full author bio